Certain heavy truck models have a passenger compartment that includes sleeping accommodation. When a driver parks his or her truck for the purpose of sleeping, and weather conditions are conducive to the use of air conditioning for cooling the passenger compartment, the engine of the truck is allowed to idle for the purpose of driving the A/C compressor. If the engine cooling fan is driven directly from the engine, rather than through an intervening fan clutch, operation of the engine will also operate the engine fan, causing cooling air to be drawn through the radiator and the A/C condenser. When the engine cooling fan is coupled with the engine through a fan clutch, operation of the fan will depend on whether the clutch is engaged or disengaged.
The fan clutch is electromagnetically operated and is selectively engaged and disengaged by a fan clutch control circuit which may comprise an A/C refrigerant pressure switch and an engine coolant temperature switch in series with the fan clutch solenoid. The circuit is typically fed from the ignition terminal of the ignition switch. The fan clutch is typically engaged when its solenoid is not being energized. In other words, the solenoid must be energized to disengage the clutch. Both the A/C refrigerant pressure switch and the engine coolant temperature switch are normally closed, meaning that when the refrigerant pressure in the A/C system is below a certain predetermined pressure above which the engine fan clutch should be engaged, the refrigerant switch is closed, and when the engine coolant temperature is below a certain predetermined temperature above which the engine fan clutch should be engaged, the engine coolant temperature switch is closed. If either the refrigerant pressure rises above this predetermined pressure or the engine coolant temperature rises above this predetermined temperature, the fan clutch solenoid will drop out, causing the fan clutch to engage and couple the fan to the engine so that the fan will operate to draw cooling air through the radiator and condenser. Stated another way, the fan clutch solenoid will be energized only when the ignition is on, and both the refrigerant pressure in the A/C system is below the predetermined pressure and the engine coolant temperature is below the predetermined temperature, whereby when the ignition is on, the fan will not be operated so long as both the refrigerant pressure is below the predetermined pressure and the engine coolant temperature is below the predetermined temperature.
Actual experience has shown that the fan clutch cycles frequently when the truck is parked with the engine idling and the A/C turned on. Such cycling tends to accelerate clutch wear and to generate extra audible noise. Accelerated clutch wear increases the operating cost of the vehicle, and the extra noise may disturb the sleep of the driver. Certain governmental regulations may also apply to the noise level, and the vehicle manufacturer must comply with any applicable regulations at the time of vehicle manufacture.
The present invention relates to an improvement for eliminating fan clutch cycling when a vehicle is parked, its engine is idling, and the air conditioning is on. The invention can be implemented in existing systems with a relatively small number of conventional electrical components. In the disclosed embodiments of the invention, these components are electromechanical switches and relays. The present invention is believed to be superior to the already known, but possibly non-compliant, expedient of simply using a bypass switch to bypass the automatic function of the existing controls for the purpose of preventing clutch cycling at idle when the air conditioning is on.
Briefly, the present invention contemplates the inclusion of a relay in the existing fan clutch control circuit. The relay may be under the control of an idle sensing switch and a parking brake switch so that when the accelerator pedal is in idle and the parking brake is set, the relay opens the feed to the fan clutch solenoid, preventing the clutch from being disengaged; however, in a presently preferred embodiment, the relay may be solely under the control of the parking brake switch relying on the engine to be in idle when the parking brake is set for any extended period with the engine running. In this way, clutch cycling is prevented when the vehicle is parked and the engine is idling. Further details of the implementation may depend on the specific vehicle involved, and so two specific implementations will be disclosed in this patent application for two different vehicles. These implementations are cost-effective ways for obtaining desired performance involving the addition of only a few conventional circuit components.
The foregoing, along with further features, advantages, and benefits of the invention will be seen in the ensuing description and claims which are accompanied by drawings. They disclose a presently preferred embodiment according to the best mode contemplated at this time for carrying out the invention.